1. Field of the Invention
The invention relates to columns of adjustable length, such as pneumatic springs of the piston-and-cylinder type, and more particularly to a column having an improved release mechanism for releasing two column members from a locked condition in which the length of the column is fixed or only variable within narrow limits.
While the invention will be described with reference to a pneumatic spring modified to constitute a support column, and such columns provide a preferred field of application for the invention at this time, it will presently become apparent that the invention is not limited to specific features of such a pneumatic spring nor to the exact nature of the column except as will be set forth hereinbelow.
2. The Prior Art
Pneumatic springs of the piston-and-cylinder type are being used widely as single legs for stools and other pieces of furniture. The piston rod may be mounted upright on a base, and a seat assembly on the cylinder, or vice versa. As long as the piston in the cylinder prevents fluid flow between the two compartments of the cylinder cavity which are separated by the piston, the height of the seat is fixed except for minor displacement permitted by resilient compression and expansion of the gas in the cylinder. When the height of the seat is to be changed, a valve connecting the compartments is opened.
For reasons of appearance and others, it is convenient to open the valve by means of a releasing rod coaxially movable in a tubular column member or element, and to move the releasing rod by means of an operating lever pivotally coupled to the releasing rod and projecting from a radial opening of the column member. Because the projecting end of the operating lever interferes with the assembly of the piece of furniture, it is usual preferred practice to insert the operating lever in the otherwise finished stool. For this reason, a known tubular column member may be of axially split construction to provide access to the radial opening for the operating lever, the two parts of the column member being joined after insertion of the operating lever. In another conventional arrangement, the radial opening is made large enough to permit free maneuvering of the lever during insertion. The first-mentioned expedient is relatively costly, and the second one makes for unsatisfactory appearance.